This invention relates to a main distributing frame ("MDF") and, more particularly, to an MDF board having a line protector for preventing associated switching equipment from overvoltage and overcurrent arising on a communication line due to lightning or contact with a power line. The inventive MDF board also has a terminal block for distributing outside cables to the switching equipment.
Recently, the electronic construction of switching systems has been rapidly promoted to cope with the diversificiation of various communication services. Particularly, electronic office switching systems have become miniaturized by the use of semiconductor devices as the structural elements, thus reducing the size of the system to be installed. Similarly, it is desirable to reduce the size of the MDF for distributing outside cables having from several thousand lines to tens of thousands of lines. Further, it is desirable for the period of time required for the completion of the system construction to be further reduced by shortening the time required for wiring of a large quantity of cables to the MDF and for mounting and installing equipment and devices on the MDF.
One example of an MDF to achieve such a requirement has been described in an article by Louis J. Scerbo et al. entitled "COSMIC II frame system: the solution to central office growth", published in April 1981 in "the Bell Laboratories Record". However, in the described MDF, a protector unit is provided with a plurality of line protectors. A connector block, for connecting jumper wires through a cable, is connected to the MDF by a manufacturing company prior to the delivery of the MDF to a switching office. Also, the connector block is mounted on a shelf at the front side of an MDF frame. The protector unit is mounted on a shelf at the rear of the frame or in a compartment; therefore, at least two people are needed for this mounting prior art equipment. On the other hand, the wiring is applied to the protector unit and the connector block through a use of wire wrapping connection by the manufacturing company. After the delivery, outside and inside cables are connected to the unit and block, the connections being made on the back surface each as rotating by a rotary mechanism. As a result, an increasing number of processes are inevitably required for the connection work, with the results that the completion of the total system installation will be prolonged. The installation space becomes larger, to limit the miniaturization of individual devices which are to be mounted on the MDF.